1. Field of the Invention
The present invention relates to an active matrix display and a manufacturing method thereof.
2. Description of the Related Art
Displays such as light-emitting diode displays and liquid crystal displays have advantageous characteristics such as decreased thickness. For this reason, these displays have been used for office equipment, computers, and the like. Recently, organic EL (Electro-Luminescent) displays have been developed, which are superior to liquid crystal displays in the following points.
1) An organic EL display is bright and self-emissive, and hence can realize a bright and clear display, a wide viewing angle, and reductions in power consumption, weight and thickness owing to a backlight-less structure.
2) An organic EL display is driven by a DC constant voltage, and hence is robust against noise.
3) The response speed of an organic EL display is on the order of μsec, whereas the response speed of a liquid crystal display is on the order of msec. Therefore, smooth moving-image display can be realized.
4) In an organic EL display, display elements can be formed by using only solid-state elements. This makes it possible to extend the operating temperature range.
Of the above displays, an active matrix display using polysilicon thin film transistors for the respective pixels, in particular, can realize excellent display characteristics.
In such an active matrix display, however, display irregularity tends to be visually recognized due to variations in the characteristics of the polysilicon thin film transistors among the respective pixels. This phenomenon is especially noticeable when display elements change their optical characteristics in accordance with the magnitude of a current flowing therethrough, like organic EL elements, and the above polysilicon thin film transistor is a drive transistor which is connected in series with the display element.
Note that Jpn. Pat. Appln. KOKAI Publication No. 11-344723 discloses a technique associated with the present invention. According to this reference, a drive circuit to be placed around a display area is composed of a normal circuit and redundant circuit, and different laser shots are used to perform laser annealing for the formation of a polysilicon thin film transistor contained in a given normal circuit and laser annealing for the formation of a polysilicon thin film transistor contained in a redundant circuit paired with the given normal circuit. In addition, the reference describes a technique of scanning a linear beam on a pixel array in an oblique direction in a laser annealing process. The reference, however, does not describe that the relative positions of polysilicon thin film transistors with respect to pixels are made different among the pixels.